The present invention relates to information recording/reproducing devices and, more particularly, to an information recording/reproducing device employing a new error correction coding method.
For information recording/reproducing devices such as magnetic disk devices, magneto-optical disk device, and compact disk devices, Reed-Solomon codes are used. This code consists of 28 elements in magnetic disk devices. A Reed-Solomon code over a Galois field GF(28) that is a set of elements for pairs, of which addition, subtraction, multiplication, and division are defined, but “divide by 0” is not defined in division, is used. This Reed-Solomon coding, in which each symbol consists of eight bits (one byte) as a unit of computing, makes error correction of signals that are recorded and reproduced.
The Reed-Solomon codes that are capable of correcting up to t symbols are constructed by including 2t redundant (parity) symbols. The length of sectors that are units of data to be recorded and reproduced at a time is 512 symbols (512 bytes). However, because the length of the Reed-Solomon codes that can be constructed over the GF(28) is not greater than 28−1=255 symbols, data is separated (interleaved) into three or more blocks and each block is constructed by the RS error correction coding. FIG. 10 shows the order of symbols including Reed-Solomon parity bytes recorded in a sector and associated RS code structures.
An advantage of the Reed-Solomon codes is that, in polynomial expression of codewords, the positions of the symbols can be arranged from the highest order αn−1, αn−2, . . . α2, α1, α0 (α: a primitive root of Galois field) and the positions of the symbols can be calculated orderly only by a multiplier during Chien search when the codewords are decoded. The Chien search is a method of evaluating an equation by assigning elements to it in order.
With a recent trend of using magnetic disk devices in video application, the International Disk Drive Equipment Material Association (IDEMA) and other organizations are discussing the usage of sectors longer than 512 bytes in a magnetic disk device, while maintaining conventional read/write processing in units of 512 bytes on the interface to the host side. One suggestion is a Reed-Solomon code organization with eight interleaving sequences that can preferably be used as an error-correcting code for data separated by a sector length of 4 Kbytes=32768 bits.
Relevant references include the following:    Non-patent Document 1: Shinji Miura, “Algebraic Geometric Codes on a Plane Curve,” the Institute of Electronics, Information and Communication Engineers Transaction (A), Vol. J75-A, No. 11, pp. 1735-1745, 1998;    Non-patent Document 2: T. Shibuya, H. Jinushi and S. Miura, “On the Performance of Algebraic Geometric Codes,” IEICE Transaction on Fundamentals, Vol. E79-A, No. 6, pp. 291-310, June 1996;    Non-patent Document 3: Shojiro Sakata “Algebraic Geometric Codes and Decoding Method Thereof,” Mathematical Sciences, No. 421, pp. 33-40, No. 422, pp. 58-60, 1998;    Non-patent Document 4: S. Sakata, “A Vector Version of the BMS Algorithm for Implementing Fast Erasure-and-Error Decoding of One-Point AG codes,” Proc. AAECC-12, Springer Verlag, pp. 291-310, 1997;    Non-patent Document 5: J. P. Hansen, H. E. Jensen, and R. Koetter, “Determination of Error Values for Algebraic-Geometry Codes and the Forney Formula,” IEEE Transaction on Information Theory, Vol. 44, No. 5, pp. 1881-1886, September 1998; and    Patent Document 1: JP-A No. 118471/2002.